The Hiller OH-23 Raven was a three-place, light observation helicopter based on the Hiller Model 360. The Model 360 was designated by the company as the UH-12 ("UH" for United Helicopters),[1] which was first flown in 1948. The OH-23 trainer was jokingly nicknamed the "Hiller Killer" by US Army Aviation student pilots who had to fly it.[2]

Contents

Development[edit]

Hiller UH-12A in 1955 when used as a crop spraying demonstrator in England

In 1947, United Helicopters developed the prototype Model 360X helicopter. A year later, on 14 October 1948 the CAA issued a production certificate for the Model 360. United Helicopters began producing the Model 360 as the UH-12. In 1949, the UH-12 became the first helicopter to make a transcontinental flight from California to New York. When Hiller upgraded the engine and the rotor blades, the company designated the new model as the UH-12A. It was the UH-12A that would be adopted by both the French and United States militaries, as well as being used by civil commercial operators in several countries.

Operational history[edit]

The H-23 Raven performed as a utility, observation, and MedEvac helicopter during the Korean War. Model numbers ranged A through D, F and G. The H-23A had a sloping front windshield. The H-23B was used as a primary helicopter trainer. Beginning with the UH-23C, all later models featured the "Goldfish bowl" canopy similar to the Bell 47.

The Raven used Hiller's "Rotor-Matic" cyclic control system, with two small servo rotor paddles offset 90 degrees to the main rotor blades. The paddles were attached to the control column, so that movement of the column would cause the pitch of the servo paddles to change, loading the main rotor blade so that the desired cyclic changes to the rotor occurred.[3] The OH-23 had a top speed of 97 mph (84 knots). The Raven had a two-bladed main rotor, a metal two-bladed tail rotor. Both the OH-23B and the OH-23C were powered by one Franklin O-335-5D engine.

Royal Navy Hiller HTMk1 (HTE-2) of 705 Squadron in 1953

The OH-23D was a purely military version with a 0-435-23C engine and a more reliable transmission. Most OH-23Ds were replaced by the OH-23G, the most common version of the Raven, with a more powerful Lycoming O-540-9A six-cylinder, horizontally opposed, air-cooled 305 hp engine. The OH-23G could seat three. The MEDEVAC version carried two external skid-mounted litters or pods. The Raven saw service as a scout during the early part of the Vietnam War before being replaced by the OH-6A Cayuse in early 1968. A Raven piloted by Hugh Thompson, Jr. played a crucial role in curtailing the My Lai Massacre. The Raven could be armed with twin M37C .30-caliber machine guns on the XM1 armament subsystem or twin M60C 7.62 mm machine guns on the M2 armament subsystem. The XM76 sighting system was used for sighting the guns.

The Royal Navy's No. 705 Training Squadron used Hiller HTE-2s for several years from 1953 and later operated Hiller 12E's for many further years as its basic helicopter trainer based at RNAS Culdrose located in Cornwall, England.

Variants[edit]

Early OH-23

Military[edit]

YH-23

One Model UH-12A, modified with two-seat cabin and 178 hp Franklin engine for US Army evaluation.[4]

H-23A

Initial production version with 178 hp (133 kW) Franklin O-335-4 piston engine and two-seat cockpit, 100 built for the US Army[5] and 5 for evaluation by the US Air Force.[6]

H-23B

H-23A with skid/wheel undercarriage and 200 hp (149 kW) O-335-6 engine (some later re-engined with a 250 hp VO-435-23B), re-designated OH-23B in 1962, 273 built for the US Army[5] and 81 for military export.

H-23C

Model UH-12C with three-seat cabin, one-piece canopy and metal rotor blades, 145 built for the US Army. Re-designated OH-23C in 1962.[5]

H-23D

H-23C with new rotor, transmission and 250 hp (187 kW) Lycoming VO-435-23B engine, 348 built for US Army. Re-designated OH-23D in 1962.[5]

H-23E

Model UH-12E, not bought

H-23F

Model UH-12E-4, four-seat model with 25-inch cabin extension and a 305 hp VO-540-A1B engine, redesignated OH-23F in 1962, 22 built for US Army.[5]

H-23G

Three-seat dual control version of H-23F, redesignated OH-23G in 1962, 793 built.[5]

HTE-1

US Navy version of the Model UH-12A with Franklin O-335 engine, two-seater with dual controls, and wheeled tricycle undercarriage, 17 built.[7]

HTE-2

US Navy version of H-23B with Franklin O-335-6 engine, 35 built.[7][8]

The 1978 film Attack of the Killer Tomatoes contains footage of a real helicopter crash. A Hiller Aircraft UH-12E, U.S. civil registry N81959, suffered a tail-rotor strike during a scene where the helicopter was supposed to have landed in a tomato patch behind police officers. The aircraft spun out of control, rolled over, and burst into flames. The helicopter pilot escaped without serious injury.[30]